1. la fuerza de rozamiento que actúa sobre un cuerpo: a) siempre se opone al movimiento
b) ninguna de las anteriores
c) es paralela a las superficies
d) es perpendicular a las superficies en contacto
2. el peso de un cuerpo es una fuerza dirigida hacia:
a) ninguna de las anteriores
b) el centro de la tierra
c) abajo
d) arriba
ayudenme porfavor a saber cual es la respuesta correcta

Your starship, the aimless wanderer, lands on the mysterious planet mongo. as chief scientist-engineer, you make the following measurements: a 2.50-kg stone thrown upward from the ground at 14.0 m/s returns to the ground in 5.70 s ; the circumference of mongo at the equator is 2.20×10^5 km ; and there is no appreciable atmosphere on mongo. (a) the starship commander, captain confusion, asks for the following information: what is the mass of mongo? (b) if the aimless wanderer goes into a circular orbit 2.20×10^4 km above the surface of mongo, how many hours will it take the ship to complete one orbit? (c) an unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 44.0 km . to the dismay of scientists on earth, an electrical fault causes an on-board thruster to fire, decreasing the speed of the spacecraft by 23.0 m/s . if nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface?

An atom that has gained or lost electrons is called an _

What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?